This invention relates to a fuel injection control method for multi cylinder internal combustion engines of the sequential injection type, and more particularly to a method of this kind which is adapted to eliminate a time lag in the supply of increased fuel to such engines at acceleration thereof for improvement of the accelerability of the engines.
In order to always achieve good operating characteristics of an internal combustion engine such as driveability, it is generally employed to detect operating conditions of the engine, determine a fuel quantity required for the detected operating condition of the engine, and supply through injection the determined quantity of fuel to the engine by means of a fuel metering system such as fuel injection valves. Fuel injection into each cylinder of the engine should be started earlier than the start of a suction stroke of the cylinder by such a period of time as to permit all the required quantity of fuel to be supplied to the cylinder even when the engine is operating in a high speed region where the valve opening period of the intake valve is small, taking into account the time required for injected fuel to form a mixture with intake air, the time required for the mixture to travel from a location of its formation in the vicinity of the fuel injection valve to the interior of the cylinder, etc.
However, if the above period of time is set to too large a value, there can occur a considerable time lag between detection of an accelerating condition of the engine and delivery of a required increased quantity of fuel into the cylinder in a low speed region of the engine in particular, thus degrading the responsiveness of the engine to the accelerating action of the driver.
To avoid such disadvantage, a method has been proposed e.g. by Japanese Provisional patent publication (Kokai) No. 58-202335, which comprises detecting whether or not the engine is in an accelerating condition, in synchronism with generation of each pulse of a control signal having a constant pulse repetition period and asynchronous with the rotation of the engine, and injecting accelerating additional fuel into all the cylinders of the engine upon detection of an accelerating condition of the engine. According to this proposed method of supplying all the cylinders with the same quantity of additional fuel, it is impossible to adjust the quantities of additional fuel to be supplied to individual cylinders. Consequently, some cylinders can become short of accelerating fuel, while other cylinders can be supplied with an excessive quantity of accelerating fuel, resulting in degraded emission characteristics of the engine.